Hah, I knew someone would eventually come around touting what an awesome idea it'd be to discharge the battery further than the kernel currently allows.
Seriously, discharge it more than the kernel currently allows. Be my guest. It'll teach you all about the discharge profile of a Li-Polymer battery before and after you hit it's avalanche voltage.
EDIT: I'll draw this out a little more. Take note, it's just off the top of my head so, choose not to believe it if you'd like. Ok, so we can set the turn off voltage to be just shy of the depletion voltage for the cell. Something around the fuzzy range of 2.5-3.1V would be the depletion voltage. Beyond this point, you'll never be able to charge the battery quite the same again. It'll fail to hold a charge for the same duration as before. Take note that this kind of inconsistent "area" is dependent on chemistry of the battery. To be on the safe side, the engineer that set the off voltage in the kernel set it to be a few hundred mV above this no doubt. I'm guessing 3.6? So sure we can go a little lower. How about 3.2? That's getting a little close for comfort...maybe 3.3V? Ok...so...let's discharge the battery for another 300mV. Are you kidding me? Keep in mind that the draw isn't linear. At these lower voltages, you'll be discharging the cell more quickly. In this 3.6V area...300mV is chump change as I understand it. My guess is you'd get maybe 20-30 minutes extra out of it. An hour maybe? Maybe it'd be fun to play around with this for your own unique phone with it's own unique battery chemistry. It's like squeezing an extra 5-10HP from an engine, eh it's always fun. But really, when you consider supplying this kind of a mod to the non-uniform masses...seriously just plug your phone in.
